1. Field of the Invention
This invention relates to an air conditioning apparatus whose capacity is adjustable according to the thermal load.
2. Description of the Prior Art
A conventional air conditioning apparatus is shown in FIG. 1, wherein a compressor 1 is driven, for example by a car engine, through a clutch mechanism (not shown) and is connected in series with a condenser 2, an accumulator 3, an expansion valve 4, and an evaporator 5. A fan 6 is disposed near the evaporator for blowing the cooled air to where it is required. A thermal sensor (not shown) is provided to detect the temperature of the air leaving the evaporator 5. The circuit from the compressor 1 to the evaporator forms a main circuit of this air conditioning apparatus. The operation of this conventional apparatus is well known, and an explanation of the heat exchange functions thereof is thus omitted.
As the rotational speed of the drive mechanism (car engine) increases, the rotational speed of the compressor 1 correspondingly increases, and the quantity of the circulating refrigerant flowing through the main circuit per unit of time increases. The work load of the evaporator 5 therefore increases, and the degree of cooling is correspondingly increased. A temperature control is thus provided, including a clutch mechanism which engages or disengages in accordance with a signal from the thermal sensor such that the compressor is caused to operate or stop in accordance with the sensed temperature. In other words, the compressor 1 operates intermittently in accordance with a signal from the thermal sensor.
The temperature of the air passing through the evaporator 5 thus undergoes large rises or falls in accordance with this intermittent operation of the compressor, and these changes in the air temperature are uncomfortable for the cars' occupants. The intermittent operation of the compressor also introduces large deviations in the load imposed on the drive mechanism. In the case of a car, particularly one of relatively small engine displacement and hence torque output, the varying load may have a substantial effect on the rotational speed of the engine, causing it to rise and fall repeatedly in accordance with the intermittent operation of the compressor.